1. Field
The following description relates to an optical coupling module for a silicon photonics chip, and more specifically, to an optical coupling module for a silicon photonics chip in which, for optical coupling at sides or inside of the silicon photonics chip, a grid is formed in an optical waveguide and a material is formed having an intermediate refractive index between a core and a cladding.
2. Description of the Related Art
FIG. 1 is a diagram showing a parallel interface method of a conventional mobile terminal, and FIG. 2 is a diagram showing waveforms for digital communication in the interface method of FIG. 1.
Recently, as a result of cost reduction, speed increase, and storage capacity expansion of optical communication systems, technology implementing a CMOS photonics-based electronic circuit portion and optical circuit portion in one chip is gradually being emphasized. This kind of technology has been continuously studied for ten years, and now businesses that use this kind of manufacturing process to provide foundry services have appeared. A silicon photonics-based optical circuit chip such as an optical multiplexer and a demultiplexer (an arrayed waveguide grating (AWG)), an optical modulator (a PN modulator, a PIN modulator, a ring modulator, an optical receiving element (a photodiode, a Ge photodiode), an optical waveguide, an optical coupler and an isolator (a Y-branch), an optical filter, an optical coupler for optical s coupling with an exterior (a grating coupler, an edge coupler), and so on, are provided as part of a library of chips fabricated by foundry businesses.
An optical circuit implemented using such an optical device is optically coupled with an external element using a grating coupler or a side coupler formed on a silicon photonics chip. The grating coupler has a larger optical alignment tolerance, but it is sensitive to wavelength. On the other hand, the side coupler works independently of wavelength, but it has a very small optical alignment tolerance. The physical size of an optical waveguide implemented on a silicon photonics chip is approximately 0.5 um×0.22 um.
Further, a refractive index of silicon, which is a core material, is about 3.5, and a refractive index of a silicon oxide, which is a cladding material, is about 1.4. Since the is difference in refractive index between the core and the cladding is considerable, and the optical waveguide is very small, external optical coupling to a single mode optical fiber is nearly impossible.
FIG. 1 is a diagram showing a grating optical coupler implemented by Luxtera of the U.S.A.
The grating optical coupler may have a grating 11 formed at one end of an optical waveguide 10, and achieve optical coupling by arranging a core 20 that is to be optically coupled in parallel with an angle (θ) at which light output from the grating 11 is refracted. As described above, the grating optical coupler may have the disadvantage of being sensitive to wavelength, and when manufacturing an optical module, it has the disadvantage of its package becoming large since it is tall.
FIG. 2 is a diagram showing a structure of a side optical coupler disclosed by a European silicon phonics study group at Ghent University. As shown in FIG. 2, the side optical coupler may have a silicon optical waveguide with an inverted taper 31, and a polymer cladding 40 formed on the inverted taper 31 and a silicon core 30, in order to gradually decrease an effective refractive index of the silicon core 30. Further, an optical signal propagates through silicon oxide located at the bottom of the silicon core 30, causing the size of an optical mode output from sides to considerably increase to approximately 3 um×3 um, thereby making it possible to achieve optical coupling with single mode optical fiber. At this time, when the optical signal propagates through the silicon oxide, optical signal loss occurs, and when performing optical coupling at the sides, additional optical signal loss occurs.